A device of the above-mentioned type intended for motor vehicles is known as a “lane-changing assistant.” The lane-changing assistant is a device for determining a risk value with the aid of locating data, in particular the distance and the relative speed of the vehicles affected by the lane change.
Lane-changing procedures involve a high risk of accident in particular on expressways and multilane freeways. The usual cause of this is that a vehicle driver who is changing lanes overlooks or incorrectly estimates the distance and/or speed of other road users who are approaching from behind in the adjacent lane or who are located in the blind spot.
A lane-changing assistant supports the driver when changing lanes, for example, during passing maneuvers and swinging-in maneuvers. Accordingly, one function of the lane-changing assistant is to inform the driver about vehicles or to warn him about vehicles that are approaching rapidly from behind or that are located in the blindspot. This helps considerably to prevent collision accidents.
The lane-changing assistant includes at least one locator, for example, a radar, lidar, or ultrasonic sensor, which monitors the rear region next to and behind the host vehicle and provides information about the vehicles affected by the lane change. The affected vehicles are in particular vehicles in the blindspot, as well as subsequent vehicles in the adjacent lane, at least the immediately subsequent vehicle.
Preferably, vehicles that are located at approximately the same level as the host vehicle and are thus not situated in the blind spot but may still be easily overlooked by the driver are also taken into account. At least with regard to subsequent vehicles, the distances of these vehicles and their time derivatives are the relevant locating data. The distance and the relative speed of the immediately subsequent vehicle are particularly relevant.
The risk value, which specifies the potential risk of a collision, is determined with the aid of the locating data. In this process, the absolute speed of the host vehicle is generally also to be taken into account, since a larger safety distance is to be maintained at higher speeds.
When the driver indicates the intention to change lanes, for example, by activating the blinker or by a steering maneuver, the lane-changing assistant generates a warning signal as a function of the ascertained risk value, in the form of an acoustic signal or in the form of an optical display on the dashboard or in the left outside mirror, for example.
If the risk value is multivalent, the warning signal is output at that moment when the risk value exceeds a particular threshold value, for example; or the warning signal specifies the risk value directly by varying the volume of the acoustic signal or in the form of a bar display, for example. Alternatively, the risk value may also be used for the purpose of enabling the lane-changing assistant to actively propose a lane change by outputting a prompt signal or, implicitly, by initiating an acceleration procedure with which preparations are made for slipping into the traffic in the adjacent lane, for example. The lane-change prompt may then also be a function of other criteria in addition to the risk value.
Furthermore, a lane-changing assistant is described in European Patent No. EP 16 12 082 A1, which, in addition to determining the movement data of the motor vehicle, also considers the environmental conditions as environmental influences that may have a favorable or an unfavorable effect on the possibilities and capabilities of other road users to react appropriately to the lane change.
In particular, relevant environmental influences are those that relate to visibility conditions and the road condition, for example, fog. The lane-changing assistant makes it possible in particular to take into account that under such conditions, the driver of the subsequent vehicle requires a larger safety distance. A large safety distance is likewise to be maintained with regard to the subsequent vehicle in the event of an unfavorable road condition, for example, a wet road surface due to rain, or slippery ice.
A detector having one or more sensors, for example, an ambient light sensor, a rain detector as is available for controlling the windshield wiper, for example, and the like, is provided for detecting the environmental conditions. Likewise, special sensors or detection systems for slippery ice and/or for fog are possible.
However, in practice, lane-changing assistants that are developed in this manner have the disadvantage that the environmental conditions determined by the detector in this manner do not always allow for an error-free inference regarding the environment. Thus, for example, the windshield may be moistened due to a cleaning of the vehicle or by a preceding vehicle such that the rain sensor indeed appropriately activates the windshield wiper function; however, the conclusion that the roadway is also wet is not accurate.
German Patent Application No. DE 103 23 639 A1 describes a method for detecting a stationary object while adaptively adjusting the detection properties of a detector. For example, ultrasonic or radar sensors are used for this purpose. In the event of stochastically occurring detection signals, such as interference signals triggered by the ground echo of gravel, for example, the detection parameters, such as the sensitivity parameters of the detector, are adjusted until these are no longer detected.
Furthermore, German Patent Application No. DE 41 20 397 A1 describes very generally a device for contact-free distance measuring, in particular for motor vehicles. The device is equipped with two ultrasonic sensors for measuring the echo time of an ultrasonic signal reflected by an object. This is used to calculate the distance to the object, the echo time of the signal between the two sensors that are disposed at a predefined distance additionally being used as a correction value.
Examples of lane-changing assistants and the associated sensor systems are described in German Patent Application Nos. DE 40 05 444 A1, DE 35 00 152 A1, DE 296 20 357 U1, DE 43 13 568 C1, DE 195 26 452 C1, U.S. Pat. No. 6,400,308 B1.